The present invention pertains to a ball-and-socket joint, preferably for motor vehicles, in which a joint ball formed on a pivot pin is mounted movably in a bearing shell consisting of a plastic, wherein the bearing shell has recesses accommodating lubricant on its inner jacket surface facing the joint ball. The bearing shell is surrounded with a housing, which accommodates it and tightly surrounds it with its inner wall.
Such ball-and-socket joints of this type are widely used in mechanical engineering, especially in the automotive industry. The frictional losses between the parts moving in relation to one another, i.e., the joint ball and the bearing shell, is reduced by the recesses provided in the joint shell, into which a lubricant reservoir is introduced before assembly, by the lubricant flowing out of the recesses into the space between the joint ball and the bearing shell in the assembled state of the ball-and-socket joints. Even though the ball-and-socket joints described have proved to be successful in practice, there is an essential problem in the fact that the lubricating film thickness between the joint ball and the bearing shell drops to values below the surface roughness of the surfaces moving in relation to one another after prolonged states of rest of the joints. As a result of this, the smoother a pivot pin, the smaller will become the lubricating film in the bearing gap. The small lubricating film thickness leads to a very great increase in the forces necessary for separation for the movement of the joint ball in relation to the bearing shell.
The above-described drawback of prior-art ball-and-socket joints is additionally facilitated by the fact that the distance between the recesses forming the individual grease pockets is usually in the range of 3-5 mm and greater, which additionally contributes to the problem that the instantaneous, rapid flow of the lubricant back into the narrow, but very long lubricating gap may become difficult in the case of movement within the ball-and-socket joint after days or weeks. Thus, the flowing away of the lubricant from the lubricating gap, which takes place over the prolonged period of rest lasting days or weeks, cannot be compensated, so that an adhesion and suction effect develops, which allows the separation forces (breakaway torque) to increase to a value several times higher than the forces occurring during continuous movement.
The object of the present invention is therefore to provide a ball-and-socket joint of this type with improved joint lubrication, which has, in particular, uniform overturning moments and torques and whose service life is thus prolonged.
This object is accomplished according to the present invention by the recesses accommodating the lubricant being grooves, which form a structural system with groove sections extending obliquely in relation to the central longitudinal axis of the ball-and-socket joint, wherein the lateral distances between two adjacent groove sections are kept short and the depth t of the groove sections is equal to or greater than the width b of the groove sections.
The solution according to which the recesses in the bearing shell are grooves which form a structural system with groove sections extending obliquely in relation to the central longitudinal axis of the ball-and-socket joint, wherein the lateral distances between two adjacent groove sections are kept short and the depth t of the groove sections is equal to or greater than one third of the width b of the groove sections has also proved to be an advantageous solution to the object described in the introduction.
Moreover, one solution may be that the recesses in the bearing shell are depressions of microscopic size.
It is achieved, e.g., by the novel design that the segments of the elastic bearing shell which are located between the groove sections are deformed during a load change and the volume of the recesses thus changes or is reduced. The lubricant present in the recesses is squeezed out of these recesses due to the reduction and it is thus available as a lubricant in the immediate vicinity of the loaded areas. Due to the hydrostatic pressure built up as a result, the lubricant squeezed out of the recesses is distributed and thus lowers the friction in the gap between the joint ball and the bearing shell. In addition, there is an advantage in that the grooves or depressions present as a structural system on the jacket surface of the bearing shell cause the entire structure of the bearing shell to be more mobile, so that e.g., peak loads of the bearing shell caused by run-out can be better distributed and thus reduced. The effective load on the ball-and-socket joint thus may possibly even increase due to the novel design of the bearing shell of the ball-and-socket joint.
If, moreover, the recesses are made microscopically small recesses, surprising improvements can also be achieved in the lubricating properties of such ball-and-socket joints as a result. The effect achieved is, on the one hand, that the recesses closed by the joint ball surface build up a static pressure as a consequence of their grease filling, and this static pressure brings about a permanent bearing effect of the ball pivot even when the joint is not moving. The above-described hydrodynamic effect is then utilized during movements of the ball pivot in order to lower the friction between the joint ball and the bearing shell.
Another essential aspect for the effectiveness of the novel ball-and-socket joint is the fact that the depth t of the groove sections is equal to or greater than the width b of these sections or one third of the width b. A pumping effect can thus be achieved within the groove sections due to the deformation of the adjoining areas of the bearing shell.
The separation torques can be brought into line with the momentums of the ball-and-socket joint by the described features according to the present invention, so that no initial breakaway torque nor the clicking noises possibly associated with same are generated after a short or prolonged period of rest. Moreover, the tendency to the jerky sliding of the parts moving in relation to one another in such joints and consequently noise generation are reduced due to the more uniform torques during different forms of movement of the ball-and-socket joint.
Moreover, the defined surface of the bearing shell consisting of a plastic contributes to a reduction in the dispersion within the production of such ball-and-socket joints.
In ball-and-socket joints whose joint ball is deflected in different directions relative to the bearing shell, the described pumping effects of the grooves can be brought about, e.g., by the longitudinal extension of the groove sections adjoining one another being arranged essentially at right angles to one another.
Another possibility of increasing the pumping effect is achieved by the structural system of the groove sections being divided into individual structural fields, in which the groove sections are arranged in parallel to one another, whereas the groove sections of structural fields located next to one another are located at right angles to one another.